Air driven tools such as hammers, riveters, or screwdrivers have been known for a long period of time. In such type of equipment, air under pressure is delivered to a turbine or air motor. The force of the air causes the motor, in the case of screwdrivers, to turn. This turning motion of the air motor may be coupled to the bit of the screwdriver to mechanically turn the bit and thus the screw or fastener which is held thereby. Various devices for selectively introducing the air to the motor are well known in the art. One such device is the throttle valve, which includes a valve body normally covering an air inlet. This valve body is released from the air inlet responsive to operator pressure against the rear of the housing of the mechanism, as when the screw is positioned at the point at which it is to be driven and force is exerted against it. Air is then forced into the air motor, causing it to turn, thereby transmitting a rotary force to the bit for purposes of driving the screw.
Screws are emplaced in the receiving chamber of the barrel in various ways. At the very outset, of course, each screw was manually positioned in the end of the barrel by hand. Various devices have been developed more recently for mechanically delivering screws into the barrel from a hopper. An example of one such prior device is set forth in applicant's prior U.S. Pat. No. 3,946,926.
Further examples of fastener feed controls for air driven screwdrivers are set forth in U.S. Pat. Nos. 3,958,614 to Bandera and 2,870,805 to Zakrzewski et al. Both of these patents are directed to mechanical devices for fastener feeding which will prevent double feeding of fasteners.
Reliable and safe fastener feeding is the object of the present invention and is believed to be the way in which the present invention departs from the prior art. The control device according to the present invention utilizes electronic circuitry to automatically effect the feeding of one and only one fastener at a time into the receiving chamber of the tool. Operation of the drive mechanism in the normal fashion only, i.e. pressure against the housing to open and close the throttle valve resets the feed circuit. Release of pressure against the housing electronically sets in motion all of the succeeding operations which are necessary to reliably feed a new fastener and return the apparatus to the ready position with a new fastener in the chamber. There is no need for any foot pedal or other safety devices which have to be activated by the feet or one of the hands. All of the safety features and the reliability measures are activated solely by the movement of the barrel rearwardly and forwardly.
In order to effect such improved fastener feeding technique, there has been built into the driving apparatus a unique electronic switching apparatus which acts responsive to movement of the barrel back and forth between the two positions which are necessary to supply air through the throttle valve into the air motor of the device. Toward this end, as the housing of the fastener driving apparatus is moved forwardly with respect to the barrel thereof (normal operation) to open the throttle valve and supply air to the air motor, an electrical switching element is engaged which resets the entire electronic circuit electronically setting everything in readiness for the ensuing fastener feeding operation. Then, as the housing moves rearwardly (responsive to release of pressure against the housing), the air supply to drive the motor is cut off and the switching element is disengaged creating an electrical signal through the control circuit.
This signal accomplishes two results in the preferred embodiment. First of all, it activates an air cylinder to blow the housing rearwardly (or the barrel forwardly) to the fastener receiving position in line with the fastener supply conduit. Secondly, a timer is activated, which upon completion of the fastener feeding will return the barrel to the normal position.
Some mention should be made here to the term "fastener receiving position". In the normal operation of air driven screwdrivers, a fastener is fed into a receiving chamber. The drive bit is then urged into engagement with the fastener slot as the operation commences. Thus when a fastener is fed, the bit is initially spaced therefrom and the fastener is loosely held by "dogs". In a preferred embodiment of the present invention the barrel is driven forward to receive a fastener, then returned to a normal or ready position with the fastener in position against and partially stabilized by the screwdriver bit. Toward this end a unique air cylinder is built into the barrel and housing to urge the barrel toward the extended position.
In general, the present invention includes a housing which carries a throttle valve, and an air motor mounted therein, and a barrel reciprocally connected thereto. The barrel is slidably received within the housing for movement between a normal, ready position, a driving position with the barrel moved rearwardly with respect to the housing; and an extended fastener receiving position in which fasteners are delivered into the receiving chamber thereof. A switching means is mounted in the housing in the path of movement of the barrel for detecting the barrel position and for causing a changed electrical condition responsive to movement of the barrel to any one of those positions. The electrical control circuit which is operated responsive to the switching means automatically effects delivery of a new fastener to the chamber responsive to the completion of the driving of the preceding fastener and unlocks the circuit for a new driving operation after a predetermined time delay.
In order to ensure that only one fastener is driven at a time, the electronic circuit must be reset by movement of the barrel to the driving position before the feeding of another fastener can occur. Then the feeding operation cannot commence until a fastener is driven and the barrel returned to the normal position.
Therefore, without any auxiliary equipment to be activated by the operator, there is provided a reliable, improved and unique fastener control system which ensures that one and only one fastener is fed into the receiving chamber of an automatic screwdriver. Further, the control apparatus with its electrical circuit ensures that a fastener cannot be fed into the receiving chamber of the barrel until the previous screw has been completely driven and is out of the tool. Fasteners are securely seated on and supported by the bit of the screwdriver prior to commencement of the driving operation.